Tumor Promotion in the Forestomach Epithelium of Mice by Oral Administration of Citrus Oils

Summary

The tumor-promoting and carcinogenic effects of lime oil, orange oil, and d-limonene on the forestomach epithelium of mice were studied. Mice, given a single dose of either 100 µg 7,12-dimethylbenz[a]anthracene (DMBA) or 200 µg benzo[a]pyrene (BP) in polyethylene glycol (PEG) by stomach tube/after food had been withheld overnight, were examined 10 weeks later and onward, and it was found that they had developed a moderate number of benign stomach tumors. Smaller single doses of DMBA (50 µg) or BP (50 or 12.5 µg) in PEG evoked fewer tumors or none. When these single doses of DMBA or BP were followed by 40 once weekly treatments by stomach tube of 0.05 ml undiluted lime oil, the tumor incidence in the forestomach was always markedly increased and in some experiments malignant tumors were induced. Treatment with lime oil, after administration of PEG only, regularly evoked a few tumors. When two intragastric doses of urethan (16 mg each) in water were given instead of DMBA or BP, a few forestomach tumors were elicited in the groups treated with lime oil. The tumor-promoting effect of lime oil was not destroyed by being heated under reflux condenser for 3 hours. Orange oil and highly purified d limonene irritated the forestomach epithelium far more than lime oil. Both induced a few tumors when given once weekly by stomach tube after a single dose of 50 µg BP in PEG. However, essentially the same result was obtained when orange oil or d-limonene was given in the same way after administration of PEG. The effects on the gastrointestinal tract of mice of lime oil administered in the diet and of orange oil added to the drinking water were also investigated. It was found that the addition of lime oil to the diet considerably increased tumor incidence following administration of a single dose of 50 μg BP and that the effect was related to the concentration of oil in the diet. Lime oil mixed with the diet appeared to be as effective in the promotion of tumors as it was when given by stomach tube after food was withheld overnight. The results with orange squash were doubtful and puzzling. Orange squash appeared to be a weak tumor promoter for the mouse forestomach, regardless of its orange oil content. Anatomical differences and considerations of dosage render it unlikely that the citrus oils are a serious tumor-promoting hazard for man.